VERY-LOW-TEMPERATURE INFRARED-LASER ABSORPTION-SPECTROSCOPY OF N2O, NO, AND NO2

We have constructed an absorption cell which is cooled to close to liq uid helium temperature by an open cycle refrigerator. Infrared spectra of gaseous N2O, NO, and NO2 cooled by collisions with helium buffer g as nearly to the cell wall temperature of approximately 5 K at pressur es near 50 m Torr have been recorded by diode laser absorption. In the present design, the probe laser beam makes four passes through the co ld sample. The enhancement of absorption line intensities is consisten t with our expectations, as is the decrease in Doppler-broadened linew idths. The sample rotational temperatures were estimated by measuring relative intensities of low-J transitions. The increased resolution re sulting from the linewidth reduction allows routine measurement of fin e and hyperfine splittings masked at the Doppler width of an ambient t emperature sample. (C) 1995 Academic Press, Inc.